Currently, as a bonding wire for semiconductor devices (hereinafter referred to as bonding wire) which connects between an electrode on a semiconductor element and an external terminal, a thin wire (bonding wire) having a wire diameter of about 20 to 50 μm is mainly used. The bonding wire is generally bonded by using an ultrasonic and thermo-compression bonding method. This method uses a general-purpose bonding device, a capillary jig connecting a bonding wire by passing the bonding wire therethrough, or the like. In order to connect the bonding wire, a tip of the wire is first heated and melted by generating arc discharge, so that a ball portion is formed by surface tension. Thereafter, the ball portion is press-bonded (ball-bonded) onto the electrode of the semiconductor element heated in a range of 150 to 300° C. Then, the wire is directly bonded (wedge-bonded) to the side of the external lead by ultrasonic compression bonding.
In recent years, the structure, material, connection technique, and the like, of semiconductor mounting have been rapidly diversified. For example, in the mounting structure, in addition to the QFP (Quad Flat Packaging) using current lead frames, new forms, such as the BGA (Ball Grid Array) and the CSP (Chip Scale Packaging) which use a substrate, a polyimide tape, and the like, are put to practical use, and a bonding wire in which loop characteristics, bonding characteristics, mass production usability, and the like are further improved is desired.
As the material of the bonding wire, high purity 4N gold (purity >99.99 mass %) has been mainly used. However, since gold is expensive, a bonding wire, which is made of other metal at inexpensive material cost, is desired.
As a bonding wire of inexpensive material cost and excellent electrical conductivity, Patent Literature 1 discloses a bonding wire which has a core material made of copper as a main component, and an outer layer provided on the core material and containing copper and a metal M different from the core material in either or both of components and composition.